- The narrow estuary is strongly tidal and is known as the Tideway. It is about mid-way protected by the Thames Barrier. East of that point it is of notable brackishness where fish, particularly in dry summers on the flood (the incoming) tide, are estuarine. It starts in south-west London at Teddington Lock and weir, Teddington/ Ham. This point is also mid-way between Richmond Lock which only keeps back a few miles of man-made head (stasis) of water during low tide and the extreme modern-era head at Thames Ditton Island on Kingston reach where slack water occurs at maximal high tide in times of rainfall-caused flooded banks.
- The head of Sea Reach – the Kent / Essex Strait – south of Canvey Island on the northern ( Essex) shore. This reach and all more eastern zones (a mixture of channels and shoals) have a width that contributes to the large, archetypal, internal but mainly submerged sandbanks. These come from a combination of silt-borne fluvial and tidal scouring and deposition ( silting).
These limiting lines have three alternates: 
- The Yantlet Line between the Crow Stone (London Stone) in Chalkwell, Westcliffe-on-Sea and another London Stone on the Isle of Grain.
- The Nore sandbank's easternmost hazardous point between Havengore Creek, Essex, and Warden Point, east Sheppey, Kent.
- Navigationally: between North Foreland, Margate, Kent via the Kentish Knock lighthouse to Harwich in Essex. Here begin sandbanks of the bight of this shallow sea. Per a Hydrological Survey of 1882–9. 
The estuary is one of the largest of 170 such inlets on the coast of Great Britain. It constitutes a major shipping route, with thousands of movements each year, including: large oil tankers, container ships, bulk carriers (of loose materials/liquids), and roll-on/roll-off (ro-ro) ferries. It is the accessway for the Port of London (including London Gateway, associated Tilbury and Purfleet) and the Medway Ports of Sheerness, Chatham and Thamesport.
The traditional Thames sailing barge worked in this area, designed to be suitable for the shallow waters in the smaller ports.
The much larger 630 MW London Array was inaugurated in 2013.
The term Greater Thames Estuary  applies to the coast and the low-lying lands bordering the estuary. These are characterised by the presence of mudflats, low-lying open beaches, and salt marshes, namely the North Kent Marshes and the Essex Marshes. Man-made embankments are backed by reclaimed wetland grazing areas, but rising sea levels may make it necessary briefly to flood some of that land at spring tides, to take the pressure off the defences and main watercourses.
There are many smaller estuaries in Essex, including the rivers Colne, Blackwater and Crouch. Small coastal villages depend on an economy of fishing, boat-building, and yachting.  The Isle of Sheppey, the Isle of Grain, Canvey Island, Two Tree Island, Havengore Island, New England Island, Rushley Island, Potton Island, Foulness Island and Mersea Island are part of the coastline. 
Where higher land reaches the coast, there are some larger settlements, such as Clacton-on-Sea to the north in Essex, Herne Bay, Kent, and the Southend-on-Sea area within the narrower part of the estuary.
The Thames Estuary is the focal part of the 21st-century toponym, the " Thames Gateway", designated as one of the principal development areas in Southern England.
The Thames Estuary 2050 Growth Commission report published in June 2018 identified the economic potential of the region. In 2020 the Thames Estuary Growth Board  was appointed, led by government-appointed Envoy Kate Willard OBE, to unlock the potential of the UK's number one green growth opportunity.
Entrepreneurs and investors have looked at the greater estuary as a possible place for a new airport,  and have expanded Southend Airport in the 2010s, which has a rail link to Fenchurch Street station, London among others.
|Official name||Thames Estuary and Marshes|
|Designated||5 May 2000|
|Reference no.||1025 |
The Thames flowing through London is an archetypal, well-developed economy urban, upper river estuary with its sedimentary deposition restricted through manmade embankments and occasional dredging of parts. It is mainly a freshwater river about as far east as Battersea, insofar as the average salinity is very low and the fish fauna consists predominantly of freshwater species such as roach, dace, carp, perch, and pike. It becomes brackish between Battersea and Gravesend, and the diversity of freshwater fish is smaller, primarily roach and dace. Euryhaline species then dominate, such as flounder, European seabass, mullet, and smelt. Further east salinity increases and conditions become fully marine and the fish fauna resemble that of the adjacent North Sea, a spectrum of euryhaline and stenohaline types. An alike pattern of zones applies to the aquatic plants and invertebrates.  
Joseph Conrad lived in Stanford-le-Hope close to the Essex marshes. His The Mirror of the Sea (1906) contains a memorable description of the area as seen from the Thames. He refers to this area in the first pages of his novel Heart of Darkness, describing it as both the launching place of England's great ships of exploration and colonization and, in ancient times, the site of colonization of the British Isles by the Roman Empire.
The form of speech of many of the people of the area, principally the accents of those from Kent and Essex, is often known as Estuary English. The term is a term for a milder variety of the "London Accent". The spread of Estuary English extends many hundreds of miles outside London, and all of the neighbouring home counties around London have residents who moved from London and brought their version of London accents with them, leading to interference with the established local accents. The term London Accent is generally avoided, as it can have many meanings. Forms of "Estuary English", as a hybrid between Received pronunciation and various London accents, can be heard in all of the New Towns, all of the coastal resorts, and in the larger cities and towns along the Thames Estuary.
For commercial shipping rounding the Nore sandbank and thus accessing Greater London, main deep-water routes were the Princes-Queens Channel and the South Channel to the south, to a lesser extent the Kings Channel and the Swin to the north. The Swin was used by barges and leisure craft from the Essex rivers, and coasters and colliers from the north east. These channels were made up of natural troughs; Yantlet Channel (Sea Reach), Oaze Deep, Knock John Channel, Black Deep/ Black Deep Channel which have been much-marked. These are separated by slow-moving sandbanks with names such as the East and West Barrows, the Nob, the Knock, Kentish Knock, the John, the Sunk, the Girdler, and Long Sand/the Long Sands. 
Shallow-bottomed barges and coasters would navigate the swatchways at flood tide, and would cross the sand banks at spitways, points where the water was least shallow, and just deep enough at that point of the tide. If they missed the moment they would heave to (lay anchor) and wait for the next tide.
Recreational craft are expected use channels most suited to the size of their vessel. Their main guide says to use when navigating to or from:
- the north: the Middle Deep, Swin, Warp and Barrow Deep. 
- the south/due east: the Horse and Gore and Four Fathom Channels. 
This table shows, from west to east, the principal navigation lights, buoys and other marks to the north (port) and south (starboard) of the main deep-water channels of the River Thames from Gallions Reach to the Sunk Light Float.      The Thames is in IALA region A so port buoys are red and starboard buoys are green.
Thames estuary navigation marks
|Name of navigational mark||South of channel||Channel||North of channel|
|Type||Light||Location coordinate||Type||Light||Location coordinate|
|Margaretness Point (or Tripcock Ness) Light||Lighthouse||Group flashing (2) white 5 s||Gallions Reach / Barking Reach||̶||̶||̶|
|Crossness Point Light||Lighthouse||Flashing white 5s||Barking Reach / Halfway Reach||̶||̶||̶|
|Crayfordness Point Light||Lighthouse||Flashing white 5s + fixed||Erith Rands / Long Reach||̶||̶||̶|
|Stone Ness Light||̶||̶||̶||Long Reach / St Clement's Reach||Lighthouse||Flashing green 2.5s|
|Broadness Point Light||Lighthouse||Occulting red 5s||St Clement's or Fiddler's Reach / Northfleet Hope||̶||̶||̶|
|Tilbury Warning Light||̶||̶||̶||Gravesend Reach||Warning light, vessels manoeuvring at Tilbury||Isophase 6s|
|Shornmead Light||Lighthouse||Group flashing (2) white, red 10s||Gravesend Reach / The Lower Hope||̶||̶|
|Ovens||̶||̶||̶||The Lower Hope||Quick flashing green|
|Haven Traffic Warning Lights||Warning light, vessels manoeuvring at Coryton||E||The Lower Hope / Sea Reach||Warning light, vessels manoeuvring at Coryton||White|
|London Gateway||̶||̶||̶||Sea Reach||Buoy|
|Sea Reach № 7||Port buoy
|Flashing Red 2.5s||The Yantlet Channel||Yellow pillar buoy||Flashing yellow 2.5s|
|Sea Reach № 6||Port buoy||Flashing red 5s||Starboard buoy||Flashing green 5s|
|Sea Reach № 5||Port buoy||Very quick flashing red||Starboard buoy||Very quick flashing Green|
|Sea Reach № 4||Port buoy||Group flashing (2) red 5s||Starboard buoy||Group flashing (2) green 5s|
|Sea Reach № 3||Port buoy||Quick flashing red||Starboard buoy||Quick flashing green|
|Sea Reach № 2||Port buoy||Flashing red 5s||Starboard buoy||Flashing green 5s|
|Sea Reach № 1||Port buoy||Flashing red 2.5s||Yellow pillar buoy
|Flashing yellow 2.5s|
|West Oaze||̶||̶||̶||The Oaze Deep||Red & white buoy||Isophase 5s|
|Oaze Bank||̶||̶||̶||Starboard buoy||Quick flashing green|
|Oaze||Yellow pillar buoy||Group flashing (4) Yellow 10s||̶||̶||̶|
|Argus||̶||̶||̶||Yellow pillar buoy yellow ‘X’ topmark||Flashing yellow 2.5s|
|Oaze Deep||̶||̶||̶||Starboard buoy||Group flashing (2) green 5s|
|Knob||Red & white buoy||Isophase 5s||̶||̶||̶|
|SE Mouse||̶||̶||̶||Starboard buoy||Quick flashing green|
|Knock John № 7||̶||̶||̶||The Knock John Channel||Starboard buoy||Group flashing (4) green 15s|
|Knock John № 5||̶||̶||̶||Starboard buoy||Group flashing (3) green 10s|
|Knock John № 4||Port buoy||Group flashing (3) red 10s||̶||̶||̶|
|Knock John № 3||̶||̶||̶||Starboard buoy||Flashing green 5s|
|Knock John № 2||Port buoy||Flashing red 5s||̶||̶||̶|
|Knock John № 1||̶||̶||̶||South cardinal buoy||Quick flashing white (6) + long flash 15s|
|Knock John||Port buoy||Group flashing (2) red 5s||̶||̶||̶|
|Black Deep № 12||Port buoy||Group flashing (4) red 15s||The Black Deep Channel||̶||̶||̶|
|Black Deep № 11||̶||̶||̶||Starboard buoy||Group flashing (3) green 10s|
|Black Deep № 10||Port buoy||Group flashing (3) red 10s||̶||̶||̶|
|Black Deep № 9||̶||̶||̶||South cardinal buoy||Quick flashing white (6) + long flash|
|Inner Fisherman||Port buoy||Quick flashing red||̶||̶||̶|
|Black Deep № 7||̶||̶||̶||Starboard buoy||Quick flashing green|
|Black Deep № 8||̶||̶||̶||West cardinal buoy||Quick flashing white (9) 15s|
|BDM2||Yellow pillar buoy (mid-channel)||Flashing yellow 2.5s||̶||̶||̶|
|Black Deep № 6||Port buoy||Flashing red 2.5s||̶||̶||̶|
|Black Deep № 5||̶||̶||̶||East cardinal buoy||Very quick flashing white (3) 5s|
|Black Deep № 4||Port buoy||Group flashing (2) red 5s||̶||̶||̶|
|BDM1||Yellow pillar buoy (mid-channel) yellow ‘X’ topmark||Flashing yellow 2.5s||̶||̶||̶|
|Black Deep № 3||̶||̶||̶||Starboard buoy||Group flashing (3) green 15s|
|Black Deep № 1||̶||̶||̶||Starboard buoy||Flashing green 5s|
|Black Deep № 2||Port buoy||Group flashing (4) red 15s||̶||̶||̶|
|SHM||Yellow pillar buoy (mid-channel) yellow ‘X’ topmark Racon T||Flashing yellow 2.5s||̶||̶||̶|
|Sunk Head Tower||̶||̶||̶||North cardinal buoy||Quick flashing white|
|Black Deep||Port buoy||Quick flashing red||̶||̶||̶|
|Trinity||South cardinal buoy||Quick flashing (6) + long flash 15s||̶||̶||̶|
|Dynamo||̶||̶||̶||Yellow pillar buoy yellow ‘X’ topmark||Flashing yellow 2.5s|
|Sunk Inner||̶||̶||̶||Light float||Isophase 3s|
- "81. Greater Thames Estuary". Countryside Agency. Archived from the original on 27 February 2006. Retrieved 2 March 2013.
- "Thames Estuary Passages" (PDF). the Cruising Almanac. Archived from the original (PDF) on 29 February 2008. Retrieved 2 March 2013.
- 2100.1 Thames Estuary South (chart), St Ives: Imray, Laurie, Norie & Wilson Ltd, February 2018. Tidal diamond "F" in West Swin
- "The Thames Estuary Partnership". Thamesweb.com. 7 February 2012. Retrieved 18 March 2012.
- "English Nature and the Greater Thames Estuary". English-nature.org.uk. Retrieved 18 March 2012.
- Ordnance Survey, Landranger map 178: The Thames Estuary (2016)
- "Home". Thames Estuary. Retrieved 4 June 2021.
- "The Thames Estuary Airport Ltd". Teaco.co.uk. Retrieved 18 March 2012.
- "Thames Estuary and Marshes". Ramsar Sites Information Service. Retrieved 25 April 2018.
- The River Thames - its geology, geography and vital statistics from source to sea, The-River-Thames.co.uk
- The River Thames - its natural history The-River-Thames.co.uk
- Eade, John. "Estuary - WHERE THAMES SMOOTH WATERS GLIDE". thames.me.uk. Retrieved 27 June 2018.
- "Recreational Users Guide" (PDF). Retrieved 27 June 2018.
- Admiralty Chart 2484 - River Thames Hole Haven to London Bridge (2013)
- Admiralty Chart 1185 - River Thames Sea Reach (2017)
- Admiralty Chart 1183 - Thames Estuary (2017)
- Crossing the Thames Estuary by Roger Gaspar (Imray)
- "Mariners' passage planning and routeing guide" (PDF).